Not really a pistol question, and not really a NFA question... bear with me. I have a SigSauer P556. I considered converting it to a SBR after setting up a trust etc... Lately I've thought more along the lines of disbanding the whole trust idea and just converting it to a rifle. Currently has a 10.5" barrel. Since stock options are not limited I'm not getting into that as a discussion point. 10.5" barrel. I'm assuming I need a 6.5" extension to bring me to a total of 16.1" with closed bolt to end of barrel. I've been searching around on the internet for a faux suppressor (larger diameter) style barrel extension and am having not a whole lot of luck finding them that are that long. I've found hollow chunks of aluminum on ebay that I could profile form etc on a lathe but that's not really what I'm wanting to do as I don't have a lathe in my non existent garage. I'm trying to stick with something I can silver solder onto the barrel as the method of permanent installation. Not really wanting to go the route of welding as that would require a steel piece and substantially more weight than aluminum depending on the size etc. I know I will have to add some weight to the already front heavy gun I'd just want to make sure I'm not adding 10lbs up there. So with that said, not completely opposed to steel like the ones listed below. Suggestions? Only things I'm finding as of lately are items like this: http://www.midwayusa.com/product/275983/dpms-flash-hider-5-1-2-length-1-2-28-thread-ar-15-matte and http://vtsupply.com/guntec-usa-5-5-flash-hider-for-10-5-uppers-us-made-steel.html Which would work, if I'm wanting to play roulette if it's long enough or not... :-/ I'd like to find something local that would allow a test fit... but that's probably unlikely. I'm not in need of the lecture either of the "rules" because I'm aware.. barrel first, THEN stock. Sucks that Red LocTite isn't considered permanent.